The subject matter described herein relates to a heat pump system and, more particularly, to a heat pump system for low temperature operation.
Existing air-to-air heat pumps generally include a supply air channel and a regeneration air channel. An energy exchange module extends between the supply air channel and the regeneration air channel. The energy exchange module transfers sensible and/or latent heat between the outside air in the supply air channel and the regeneration air in the regeneration air channel. The supply air channel and the regeneration air channel also include heat exchangers. The supply air channel includes a supply air heat exchanger and the regeneration air channel includes a regeneration air heat exchanger. The supply air heat exchanger and the regeneration air heat exchanger are in fluid communication through a refrigeration system to further transfer heat between the outside air and the regeneration air. In a winter mode, heat and/or moisture in the regeneration air is transferred to the outside air to generate heated and/or humidified supply air that is discharged from the supply air channel. During a summer mode, heat and moisture in the outside air is transferred to the regeneration air to generate cooled and dehumidified supply air that is discharged from the supply air channel.
However, conventional heat pump systems are not without their disadvantages. During winter modes, when the outside temperature has dropped below approximately 35° F./33° F., frost may form on the coils of the regeneration air heat exchanger. Accordingly, the heat pump system must be shut down so that the coils can be defrosted. During the time period that the heat pump system is shut down, the building incorporating the heat pump system must go without a heat source or requires an auxiliary heat source or recirculated air. Additionally, during summer modes, the regeneration air heat exchanger may be required to supply large amounts of heat to the regeneration air. As a result, an efficiency of the regeneration air heat exchanger may decrease substantially.
A need remains for a means to preheat the regeneration air during winter modes to prevent frost formation on the regeneration air heat exchanger at temperatures below approximately 35° F./33° F. Another needs remains to increase the efficiency of the regeneration air heat exchanger by lowering the condensation temperature during the summer mode using a pre-processing module in the regeneration air.